From artificial neural networks to spiking neuron populations and back again.

In this paper, we investigate the relation between Artificial Neural Networks (ANNs) and networks of populations of spiking neurons. The activity of an artificial neuron is usually interpreted as the firing rate of a neuron or neuron population. Using a model of the visual cortex, we will show that this interpretation runs into serious difficulties. We propose to interpret the activity of an artificial neuron as the steady state of a cross-inhibitory circuit, in which one population codes for 'positive' artificial neuron activity and another for 'negative' activity. We will show that with this interpretation it is possible, under certain circumstances, to transform conventional ANNs (e.g. trained with 'back-propagation') into biologically plausible networks of spiking populations. However, in general, the use of biologically motivated spike response functions introduces artificial neurons that behave differently from the ones used in the classical ANN paradigm.

From knowing what to knowing where: modeling object-based attention with feedback disinhibition of activation.

We propose a neural model of visual object-based attention in which the identity of an object is used to select its location in an array of objects. The model is based on neural activity observed in visual search tasks performed by monkeys. In the model, the identity of the object (target) is selected in the higher areas of the ventral stream by means of a cue. Feedback activation from these higher areas carries information about the identity of the target to the (lower) retinotopic areas of the ventral stream. In these areas, the feedback activation interacts with feedforward activation produced by the object array. The interaction occurs in local microcircuits, and results in a selective activation on locations in the retinotopic areas of the visual stream that correspond to the location of the target in the object array. The selective activation consists of a form of gain control, produced by disinhibition. Transmitted to the dorsal stream, this activation directs spatial attention to the location of the target. In this way, an action directed at the target can be generated.

Trial of labour after previous caesarean section in rural Zimbabwe.

OBJECTIVE: Vaginal delivery after previous caesarean section is widely accepted in Western countries. Is a trial of labour in rural Africa also safe for mother and child? STUDY DESIGN: In a case control study in rural Zimbabwe the outcome of labour of 281 women who had one or more previous caesarean sections was compared with 4501 women who had no previous caesarean section. Maternal and perinatal mortality, the percentage of vaginal birth and factors related to the achievement of vaginal delivery were studied. Data were tested for statistical significance with a Mantel-Haenszel equation for odds ratio's. RESULTS: No elective caesarean sections were performed. After previous caesarean section, 124 (44%) out of 281 women had a vaginal birth. One scar rupture occurred in a woman with thyrotoxicosis. Perinatal and maternal outcome did not differ significantly between cases and controls. A history of more than one previous caesarean section (Odds Ration (OR) = 10.0; 95% Confidence Interval (CI95%) = 4.4-23.8) or a previous caesarean section for cephalopelvic disproportion (OR = 6.2; CI95% 3.2-120) increased the risk for a repeat caesarean section significantly. CONCLUSION: A policy to allow all women a trial of labour after a previous caesarean section did not increase adverse pregnancy outcome. Also in rural Africa it seems rational to encourage a trial of labour after one or more previous caesarean sections.

On the statistical independence of color and shape in object identification.

M. J. Nissen (1985) showed that color and shape are processed independently. M. A. Monheit and J. C. Johnston (1994) argued that dependence of color and shape in these experiments was reduced due to random guessing. They conducted 4 experiments in which they attempted to reduce the effect of random guessing. A strong dependence of color and shape reports was observed. In this article the effects that random guessing can have on statistical (in)dependence are analyzed. The authors argue that Monheit and Johnston's analysis is incorrect and inconsistent with the data they report and that random guessing can be the cause of statistical dependence of color and shape reports.

Evaluation of motility enrichment on modified semisolid Rappaport-Vassiliadis medium (MSRV) and automated conductance in combination with Rambach agar for Salmonella detection in environmental samples of a milk powder factory.

The efficacy of motility enrichment on modified semisolid Rappaport-Vassiliadis medium (MSRV) and an automated conductance method for the detection of Salmonella in environmental samples was evaluated. Two hundred and ten environmental samples from unrestricted areas of a milk powder factory, 49 of which were artificially contaminated with Salmonella infantis, were examined. From exactly 100 samples Salmonella could be isolated. With the conventional (ISO-DIS 6579) method a 100% score was obtained, whereas the MSRV method gave 82 positive results. The conductance method permitted the detection of Salmonella in only 66 samples. The use of Rambach agar improved isolation efficiency of Salmonella from enrichment broths.

Perceiving AIDS-related risk: accuracy as a function of differences in actual risk.

This study investigates the perceived risk of an HIV infection. Cognitive antecedents of biases in risk perception and their effects on behavioral intentions were investigated. The purpose of this study was to determine the relative accuracy of risk assessments for samples that vary in actual risk for AIDS. Subjects were citizens of Amsterdam, heterosexuals with private partners, gay men, and heterosexuals with prostitution partners. Although optimistically biased in all samples, perceptions of risk were related to previous risk behavior in high-risk samples only. Pessimism was more pronounced in samples higher at risk. Optimists had lower levels of previous risk behavior and increased intentions to adopt safe sex practices. Ss in samples higher at risk had, therefore, relatively adequate perceptions of risk.

An element in the visual field is just a conjunction of attributes: a critique of Bundesen (1991)

Nissen (1985) presented results showing that in partial-report experiments, selection by location was different from selection by color or by shape. Bundesen (1991) presented a reinterpretation of these results, claiming that they can also be explained by a model in which location selection is treated on a par with selection by color or by shape. We will show that the analysis given by Bundesen is based on a special relation between an "element" in the visual field and its location, which in fact reduces the expressions given by Bundesen to those given by Nissen. Furthermore, we will show that in Bundesen's theory, it is assumed that in the process of perceptual categorization an element in the visual field can be referred to without the use of one of its attributes. This assumption is untenable from a theoretical point of view. In all, the results presented by Nissen can still be regarded as evidence for the difference between selection by location and selection by color or by shape.

Is the brain an effective Turing machine or a finite-state machine?

A theorem presented by Hornik, Stinchcombe, and White (1989) suggested the possibility that connectionist networks could be effectively Turing machines. Levelt (1990) argued that the theorem of Hornik et al. only implies that networks are finite-state machines and are therefore not capable of generating the very unlimited productivity of symbol systems. Yet it can be argued that all real machines, including the brain, are finite-state machines. If so, no real machine actually possesses the very unlimited productivity of symbol systems. So any model of actual behaviour should capture the limitations on productivity inherent in the situation. Thus connectionist networks can be valuable models in psychology, precisely because they are finite-state machines.

The importance of ethnicity as a risk factor for STDs and sexual behaviour among heterosexuals.

OBJECTIVES: To study risk factors for sexually transmitted diseases (STDs) and sexual behaviour. Especially to assess whether there is a higher risk of being infected with STDs among ethnic minorities, and if so for what reasons. SETTING: STD-clinic of the Municipal Health Service of Amsterdam, the Netherlands. SUBJECTS: Cross-sectional study of heterosexuals (255 men and 343 women) with multiple sexual partners, who participated between October 1987 and January 1990. RESULTS: Besides STD-related complaints, ethnicity was an important independent predictor of one or more diagnosed genital STDs. STD-prevalence was higher among men born in Turkey (47%, OR = 3.4) and men born in Surinam (36%, OR = 2.1), compared with Dutch men (21%). While Turkish men had mainly riskful sexual behaviour with prostitutes, Surinam men had more often riskful sexual contact with private partners. Among women, STD prevalence was higher among West-European (38%, OR = 2.3) and Latin-American women (30%, OR = 1.6), compared with Dutch women (21%). Latin American women had more often riskful sexual contact with clients; sexual behaviour of West-European women was riskful with both clients and private partners. CONCLUSIONS: Prevention activities should be directed at specific sexual and ethnic groups, sources of information should be carefully selected, and some groups should be addressed differently with regard to language but to content as well.

AIDS-related health behavior: coping, protection motivation, and previous behavior.

The purpose of this study was to examine Rogers' protection motivation theory and aspects of Janis and Mann's conflict theory in the context of AIDS-related health behavior. Subjects were 84 heterosexual men and women and 147 homosexual men with multiple sexual partners; LISREL's path-analysis techniques were used to evaluate the goodness of fit of the structural equation models. Protection motivation theory did fit the data but had considerably more explanatory power for heterosexual than for homosexual subjects (49 vs. 22%, respectively). When coping styles were added, different patterns of findings were found among both groups. Adding variables such as social norms and previous behavior increased the explained variance to 73% for heterosexual subjects and to 44% for homosexual subjects. It was concluded that although protection motivation theory did fit the data fairly adequately, expanding the theory with other variables--especially those related to previous behavior--could improve our understanding of AIDS-related health behavior.

PIP: In this AIDS related health behavior study, the conceptual framework is similar to Rogers' protection motivation theory with elements from Janis and Mann's conflict theory. The purpose of the study is to examine the effects of cognitive mediators on behavioral intentions, to examine the relationship between the mediators and adaptive and maladaptive coping styles, and to test the predictive validity of mediators with additional variables. The adaptive style is included as vigilance, which refers to accurate information searching, and problem solving to reduce and minimize the threat. 2 maladaptive styles are included as defense avoidance (denying threatening information or evading the thread actively) and hypervigilance (panic-like searching for appropriate responses without reaching well balanced decisions). Additional variables included that ordinarily are not found in the general framework of protection motivation and conflict theory are fear, disadvantages of the adaptive response, pleasantness of the maladaptive response, social norms and previous behavior, knowledge about a threatening situation, perceived constraints, and regrets about previous maladaptive behavior. 147 homosexual and 84 heterosexual subjects, who were analyzed separately, aged 18-30 and not HIV positive were recruited in Amsterdam. Self administered questionnaires were given which assessed sexual behavior and intentions, threat and coping appraisal, coping styles, and additional variables. The program, LISREL, was used to provide maximum likelihood estimates and Chi square tests. Differences between groups were pronounced. Homosexuals perceived themselves more at risk and social norms more positive, felt more fear, had lower levels of self response efficacy, and greater tendency for previous adaptive behavior and higher behavioral intentions. There was confirmation of other findings that coping appraisal processes independently affect behavioral intentions to adopt the recommended response. Severity, for example, was significantly related to behavior only when fear as worry was removed from the equation, and risk reduction motivation varied with worry, even when threat appraisal processes are held constant. Hypervigilance had neither adaptive nor maladaptive influences. For planning purposes, it is suggested that information programs need to emphasize how to handle constraining situations. Population specific messages which can be sensitive to severity or experience with the threat need consideration. Immediate positive effects of recommended behavior is suggested. Motivational factors are important at higher fear levels, where anxiety reduction is the focus instead of danger avoidance. Prevention needs to minimize fear arousal. Limitations included the lack of reciprocal models and a limited behavioral intentions scale.

Limited changes in sexual behaviour of heterosexual men and women with multiple partners in The Netherlands.

To study changes in sexual behaviour, heterosexuals with multiple sexual partners were recruited through an STD-clinic and asked to return every 4 months for follow-up. Between October 1987 and June 1989, 512 heterosexuals entered the study and 140 men and 200 women had at least one follow-up visit. No changes were found between 3 visits in the kind of sexual techniques practiced. Condom use during vaginal intercourse with commercial partners (prostitutes or clients) was relatively high and remained high, but was low and remained at that level with private partners. Men and women reduced their number of private sexual partners by 50%, but the decline in the number of commercial partners was nonsignificant. Although more information is needed about the underlying social-psychological aspects of behavioural change, it seems necessary to redesign prevention activities to stress the effectiveness of condoms and to encourage condom use especially among heterosexuals with multiple private partners.

[HIV prevalence among heterosexual subjects with multiple partners in Amsterdam]. / HIV-prevalentie onder heteroseksuelen met veel wisselende partners in Amsterdam.

To study the prevalence of HIV-infection among heterosexuals with multiple partners, participants were recruited from a STD clinic in Amsterdam. In 1988, 785 visitors met the selection criteria, of whom 361 (46%) finally participated. An HIV prevalence of 2/361 (0.6%) was found among participants. To test representativity, participants and refusers were compared on demographic characteristics and prevalence of STDs. Male refusers were on average younger, had on average fewer partners and relatively more often had a foreign nationality. Female refusers had on average fewer partners. No differences were found in the prevalence of STDs between participants and refusers. Because of the high refusal rate and differences between participants and refusers, the HIV prevalence found is not representative of heterosexuals with multiple partners.

Context-dependent migrations in visual word perception.

In the present study we investigate the effect of context--that is, a prime--on migration errors. Migration errors, or migrations, are caused by perceptual interactions between two words in a visual display, such as line-lace. After postcuing, subjects sometimes report lane or lice, instead of the requested word line. This phenomenon has been demonstrated by previous studies. In the experiments reported here, we replicate this phenomenon. We also find that more migrations of the lane type occur (compared with lice type), when the display line-lace is preceded by a prime related to lane (but not to lice). This shows that higher order word knowledge, in the form of semantic relations between words, influences the migration phenomenon. Further, we show that the number of migration errors are not a result of only a summation of activation from the letters in the display. The method we developed to isolate context-dependent migrations also gives valuable information about the effect of contextual information on word perception.